In electrophotographic applications, such as xerography, a charge retentive surface is electrostatically charged and exposed to a light pattern of an original image to be reproduced to selectively discharge the surface in accordance therewith. The resulting pattern of charged and discharged areas on that surface form an electrostatic charge pattern (an electrostatic latent image) conforming to the original image. The latent image is developed by contacting it with a finely divided electrostatically attractable powder referred to as "toner". Toner is held on the image areas by the electrostatic charge on the surface. Thus, the toner image is produced in conformity with the light image of the original being reproduced. The toner image may then be transferred to a substrate such as paper, and the image affixed thereto to form a permanent record of the image to be reproduced. Subsequent to development, excess toner left on the charge retentive surface is cleaned from the surface. The process is well known and useful for light-lens copying from an original and printing applications from an electronically generated or stored original, where a charge surface may be imagewise discharged in a variety of ways. Ion projection devices where a charge is imagewise deposited on a charge retentive substrate operate similarly. In a slightly different arrangement, toner may be transferred to an intermediate surface, prior to retransfer to a final substrate.
Although a preponderance of toner forming the image is transferred to paper during transfer, some toner invariably remains on the charge retentive surface, it being held thereto by relatively high electrostatic and/or mechanical forces. Additionally, paper fibers, Kaolin and other debris have a tendency to be attracted to the charge retentive surface. It is essential for optimum operation that the toner remaining on the surface be cleaned thoroughly therefrom. A commercially successful mode of cleaning employed in automatic electrophotography utilizes a brush with soft conductive or insulative fiber bristles. While the bristles are soft, they are sufficiently firm to remove residual toner particles from the charge retentive surface. In addition to relying on the physical contact of the brush with the surface for the removal of toner, it has been found that establishing an electrostatic field between the charge retentive surface and the cleaning member enhances toner attraction to the cleaning brush fibers. The creation of the electrostatic field between the brush and charge retentive surface is accomplished, in the case of conductive fibers, by applying a D.C. voltage to the brush. When the fibers forming the brush are electrically conductive and a bias is applied thereto, cleaning is observed to be more efficient than if the fibers are non-conductive or insulative. U.S. Pat. No. 4,819,026 to Lange et al. discloses an electrostatic cleaning brush of the type described, to which a bias is applied to conductive fibers to electrostatically enhance cleaning of the charge retentive surface. In the case of insulative fibers, the electrostatic field between the charge retentive surface and the cleaning member is achieved by selecting fibers, flicker bars and toner material that cause the brush to triboelectrically charge to the desired electrical potential.
In certain electrophotographic processes, particularly in highlight color applications that provide two types of toner to develop latent images on a surface, a phenomena of filming is noted. Filming is characterized by the tenacious adherence of very fine material, including toner residues, toner additives (and particularly anti-caking additives), and paper debris to the charge retentive surface. For reasons that are not completely understood, standard conductive and insulative brush cleaners do not provide effective cleaning in systems where a high degree of filming is present. Film cleaning can sometimes be improved in brush cleaners by stiffening the brush fibers, but usually the film remains on the surface. Filming is not noted in association with all toners. Particular toners appear to cause filming, while other toners do not seem to have filming associated with their use. In a particular arrangement, toner filming is noted with the highlight color toner containing anti-caking and other surface additives, described in U.S. patent application Ser. No. 07/342,132 filed Apr. 24, 1989, entitled "Process for Forming Two-Color Images", by Koch et al., but is not noted with the black toner which does not contain any surface additives also described therein. Filming becomes a particular problem when highlight color toner is used for a large proportion of a document, and/or for a large number of copies.
To alleviate the filming problem, an abrasive surface may be used to remove the film. Accordingly, U.S. Pat. No. 4,870,465 to Lindblad et al shows an auger arrangement providing porous foam or poromeric surfaces or surfaces filled with abrasive material for the removal of film buildup. Dual foam rolls with porous surfaces have also been proposed, in U.S. Pat. No. 3,807,853 to Hudson. Poromeric materials tend to collect toner in the pores of the material, which in movement past the charge retentive surface have the tendency to abrade or scour the surface. A light scouring or abrading action is desirable, but too heavy a scouring action will tend to damage coatings on the charge retentive surface. When a foam roll is arranged to provide an adequate cleaning function, it proves to be excessively abrasive, and may damage a soft photoconductive layer on a charge retentive surface. U.S. Pat. No. 4,878,093 to Edmunds shows the combination of a brush and foam roll.
U.S. Pat. No. 4,673,284 to Matsumoto et al. discloses a cleaning device with a rotatable cleaning brush with two types of fibers mounted on a cylindrical core. Among the embodiments shown, are a combination of fibers, of poly-4-fluoroethylene fibers (Teflon) and rayon. U.S. Pat. No. 3,780,391 to Leenhouts shows a cleaning brush fixed in a vacuum chamber, with a flicker bar used to apply a potential to the brush opposite that of residual toner particles which are to be removed from the photoconductive surface. U.S. Pat. No. 4,123,154 to Fisher discloses a cleaning apparatus wherein a flicker element removes residual material from a cleaner element. The flicker element works together with a corona charging device to neutralize toner to aid in removal from a cleaning element. U.S. Pat. No. 4,435,073 to Miller shows a cleaning brush with a plurality of flicker bars, at least one of which is fabricated from a material that will cause the charge on the brush to reverse at least once for every revolution of the brush, such reversal taking place while the brush fibers are subject to a toner removing airflow.
It is known to place a test patch in an interdocument area of the imaging member in an electrostatographic device for the purpose of testing machine operating conditions.
The references cited herein are all incorporated by reference for their teachings.